The overall goal of this application is to understand how the vertebrate retina forms organized layers. We are proposing a novel integrative approach in zebrafish to address what are the essential molecules, critical cell types, and important cellular behaviors that facilitate proper cell fate and positioning within the retina. Previously we have isolated mutations in zebrafish which specifically disrupt retinal lamination. We have also taken advantage of the transparency of zebrafish embryos to establish techniques which allow us to track individual cells in vivo as the retina develops. This application proposes experiments that combine these two experimental tacts: mutation analysis and cell behavior studies. The focus of this application is on the period from when a proliferating retinoblast enters its last cell cycle to when it completes migration away from the verticular zone. This encompasses the time when cells become specified to particular cell types to when laminar position is established. In accordance with our goal, the early lamination mutations which affect this developmental stage (disarrayed, bewildered, perplexed, and young) and the cellular behaviors that occur during this transition (interkinetic nuclear migration, final cell division orientation, and post-mitotic cell migration) will be systematically studied. In addition, we will use molecular genetics to identify the mutated genes. Because the genes and cells that are utilized during development invariable have maintenance roles within the adult, and therefore underlie pathogenic states--our studies can provide insights into mechanisms that lead to retinal diseases.